Electric motor vehicle coolant pumps are used, for example, in supercharged air cooling and engine cooling so as to realize a cooling corresponding to respective requirements, in particular, in the cold start phase. This results in reduced fuel consumption and in a corresponding reduction of exhaust gas emissions.
Such a coolant pump is described, for example, in DE 101 33 936 A1. The coolant pump described therein comprises an integrally-formed and rotatably-supported rotor made from an injection molded plastic material. The rotor comprises a pump rotor section with a plurality of arcuate rotor blades projecting radially from a pump rotor bottom. The rotor further comprises a motor rotor section which is a part of an electric drive motor. The entire rotor is made from a polyamide or polyphenylene sulphide plastic material and a finely dispersed admixture of permanent magnet. Such a plastic material/permanent magnet material mixture has a reduced mechanical stability relative to a pure plastic material so that with such a rotor structure, the material thickness of the rotor blades must be chosen to be correspondingly thick in order to endure the mechanical stresses and to guarantee a safe operation. As a consequence, the available flow cross section of the pump rotor channels between the rotor blades is rather small, whereby the efficiency of the rotor is compromised. For reasons of process engineering, an integrally-formed rotor can moreover be produced by injection-molding only with axially distally open pump rotor channels. A pump rotor with distally open pump rotor channels has a reduced hydraulic performance, so that the efficiency of the rotor is also thereby reduced.